1. Field of the Invention
The present invention relates to an impact tool such as an impact driver that has an anvil protruding frontward from a housing and makes the anvil generate a rotational impact force.
2. Description of Related Art
A conventional impact tool such as impact driver, as disclosed in Japanese Patent Application Publication No. 2003-231067, includes a spindle, an anvil, and an impact mechanism. The spindle is rotatable in a housing by means of a motor. The anvil is supported on the front side of the spindle to be rotatable coaxially with the spindle. A front end portion of the anvil, at which a tool bit is to be attached, protrudes frontward out of the housing. The impact mechanism transmits rotation of the spindle to the anvil as a rotational impact.
The impact mechanism includes a hammer, balls, and a coil spring. The hammer is fitted on the spindle such that the hammer is movable in the front-back direction, and has an annular groove disposed on a rear surface thereof. The balls are disposed in or between cam grooves disposed on the spindle and the hammer. The coil spring is inserted from its front end into the annular groove of the hammer to bias the hammer to an advanced position of the hammer to engage the hammer with the anvil. When the spindle is rotated, for instance for screwing, the hammer is rotated integrally with the spindle via the balls to rotate the anvil. When a load applied to the anvil increases, rearward movement of the hammer occurs against the biasing force of the coil spring because of the balls being rolled rearward along the cam grooves. Consequently, the hammer is disengaged from the anvil. After thus disengaged, the hammer being rotated is again engaged with the anvil by the biasing force of the coil spring with the balls being rolled frontward along the cam grooves. The engagement and disengagement of the hammer with and from the anvil is repeated so that a rotational impact is intermittently applied to the anvil.
A carrier portion of planetary gears is disposed on the rear side of the spindle of the impact tool, and a washer is disposed frontward of the carrier portion to receive a rear end of the coil spring biasing the hammer. The washer has an outer peripheral portion with which the rear end of the coil spring is held in contact, and a frontward extended portion circumferentially disposed at an inner circumference of the outer peripheral portion and fitted on the coil spring so as to inhibit radially inward contraction or deformation of the coil spring. Since the frontward extended portion of the washer is located on the rear side of the hammer, it is required in designing the impact tool to locate the range of the stroke of the hammer frontward of the washer such that when backward moved or retracted the hammer does not contact the frontward extended portion of the washer. This makes the axial dimension of the impact tool relatively large.